Acrylonitrile-based precursor fiber for carbon fiber and method for production thereof

Abstract

This invention relates to an acrylonitrile-based precursor fiber for carbon fiber which is prepared from an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, and which is characterized by a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (pi) of not less than 90% as determined by wide-angle X-ray analysis, and a degree of variation in tow fineness of not greater than 1.0%. This precursor fiber has a high strength, a high elastic modulus, a high degree of denseness, a high degree of orientation, and a low degree of variation in tow fineness, and can hence be used to form a high-quality carbon fiber inexpensively by oxidation for a shorter period of time.

What is claimed is:  
     
       1. An acrylonitrile-based precursor fiber of an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, said acrylonitrile-based precursor fiber having a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (π) of not less than 90% as determined by wide-angle X-ray analysis, and, when made into a tow, a degree of variation in tow fineness of not greater than 1.0%. 
     
     
       2. An acrylonitrile-based precursor fiber as claimed in  claim 1  wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units. 
     
     
       3. An acrylonitrile-based precursor fiber as claimed in  claim 1  which has been formed by the wet spinning process. 
     
     
       4. A process for preparing an acrylonitrile-based precursor fiber as claimed in  claim 1 , which comprises the steps of wet-spinning an acrylonitrile-based copolymer to form a coagulated fiber, subjecting the coagulated fiber to primary drawing comprising in-bath drawing or a combination of in-air drawing and in-bath drawing, and subjecting thus obtained fiber to secondary drawing involving pressurized steam drawing, wherein the temperature of the heating roller located immediately before the introduction of the fiber into a pressurized steam drawing machine is adjusted to 120-190° C., the degree of variation of steam pressure in said pressurized steam drawing is controlled so as to be not greater than 0.5%, and the coagulated fiber is drawn in such a way that the proportion of the secondary draw ratio to the overall draw ratio is greater than 0.2. 
     
     
       5. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 4  wherein the overall draw ratio is not less than 13. 
     
     
       6. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 4  wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units. 
     
     
       7. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 4 , wherein, prior to drawing, the coagulated fiber has an elastic modulus in tension of 1.1 to 2.2 cN/dtex. 
     
     
       8. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 4  wherein said pressurized steam drawing is carried out at a steam pressure of not less than 200 kPa (gauge pressure). 
     
     
       9. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 4  wherein the fiber subjected to said pressurized steam drawing has a moisture content of not greater than 2% by weight. 
     
     
       10. A carbon fiber formed by oxidation and carbonizing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 1 . 
     
     
       11. An acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 2  which has been formed by the wet spinning process. 
     
     
       12. A process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 5  wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units. 
     
     
       13. The process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 12  wherein, prior to drawing, the coagulated fiber has an elastic modulus in tension of 1.1 to 2.2 cN/dtex. 
     
     
       14. The process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 13  wherein said pressurized steam drawing is carried out at a steam pressure of not less than 200 kPa (gauge pressure). 
     
     
       15. The process for preparing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 14  wherein the fiber subjected to said pressurized steam drawing has a moisture content of not greater than 2% by weight. 
     
     
       16. A carbon fiber formed by oxidation and carbonizing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 2 . 
     
     
       17. A carbon fiber formed by oxidation and carbonizing an acrylonitrile-based precursor fiber for carbon fiber as claimed in  claim 3 . 
     
     
       18. A tow consisting of acrylonitrile-based precursor fibers prepared from an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, said acrylonitrile-based precursor fiber having a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (π) of not less than 90% as determined by wide-angle X-ray analysis, and a degree of variation in tow fineness of not greater than 1.0%. 
     
     
       19. A tow as claimed in  claim 18  wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units. 
     
     
       20. A tow as claimed in  claim 18  which has been formed by a wet spinning process. 
     
     
       21. A tow as claimed in  claim 19  which has been formed by a wet spinning process. 
     
     
       22. An acrylonitrile-based precursor fiber of an acrylonitrile-based copolymer containing 96.0 to 98.5% by weight of acrylonitrile units, said acrylonitrile-based precursor fiber having a tensile strength of not less than 7.0 cN/dtex, an elastic modulus in tension of not less than 130 cN/dtex, an iodine adsorption of not greater than 0.5% by weight based on the weight of the fiber, a degree of crystal orientation (π) of not less than 90% as determined by wide-angle X-ray analysis. 
     
     
       23. An acrylonitrile-based precursor fiber as claimed in  claim 22  wherein said acrylonitrile-based copolymer is composed of 96.0 to 98.5% by weight of acrylonitrile units, 1.0 to 3.5% by weight of acrylamide units, and 0.5 to 1.0% by weight of carboxyl-containing vinyl monomer units. 
     
     
       24. An acrylonitrile-based precursor fiber as claimed in  claim 22  which has been formed by a wet spinning process. 
     
     
       25. An acrylonitrile-based precursor fiber as claimed in  claim 23  which has been formed by a wet spinning process.